Amanda Bynes' parents have obtained a conservatorship over the star after telling a judge that the actress has spent huge amounts of money buying jewellery for total strangers, according to US reports.

In legal documents obtained by TMZ, Rick and Lynn say the star is at "substantial risk" to herself and others, citing erratic behaviour including her DUI arrest last month.

The documents also show that the 28-year-old actress is spending "alarming amounts" of money. She's reportedly worth $5, 747, 703 and her parents say her purchases have been "extensive".

Doctors treating the Easy A star, who was committed to a psychiatric treatment facility in Pasadena, California early this month, secretly convinced a judge on Monday to extend her involuntary hold because the 28-year-old star is still "very ill" and unable to take care of herself.

If the extension wasn't granted, the blonde beauty could have walked out of the hospital on Monday, according to gossip website TMZ.com.

(Image: Barcroft / Splash)

Amanda spent five months in a treatment facility in July 2013 when she was placed under involuntary psychiatric hold.

She was released in December and appeared to be getting her life back on track until a conservatorship giving her mother control of her affairs came to an end last month.

Another source recently revealed doctors may go to court to obtain an LPS hold, which would allow medics to confine her to hospital or another secure facility and administer medication against her will and lasts up to 12 months.